Theory shows (see pages 30 to 35 herein, per E. S. Taylor ref) that the log-spiral with heretofore conventional side-walls does not represent an inviscid, steady-state source-vortex flow path in a vaneless diffuser. Further, the weight of experimental evidence researching annular vaned diffusers having log-spiral vanes with conventional side-walls, is that the isobar at the throat is normal or nearly normal to the vanes. (Also, irrelevant here, it is normal with straight passages, per theory.)
On the other hand, for steady-state inviscid flow, the isobar at the entrance to a vaneless diffuser is a concentric great circle about the impeller-diffuser center axis, that is, extremely oblique to the flow direction there.
Thus, this means that there has existed for about 47 years, an abrupt deflection of the gas flow direction by one side of the vane or the other or both, in a very short distance, in effect a shock-treatment, sub or supersonic, which creates a loss in efficiency of the diffuser as a whole.
This inventor has long maintained that if one could only achieve highly oblique isobars at the throat, then one could design for a gradual transition from the then resulting highly oblique isobar at vane-tip circle to a normal one near the passage exit, for much more gentle treatment of the high velocity gas, resulting in higher efficiency overall of the diffuser.
The purpose of this invention is to achieve such highly oblique isobars at the "throat". That is now accomplished herein, resulting in a most obviously drastically new and different structure, on which structure only, the claims herein are based, the claims not written on the theory which alone begets this structure, though that theory is fully disclosed herein.
The example of design computed herein is for inviscid steady-state flow only, thus not making allowances for the heretofore experimentally established deleterious effects on performance of viscosity and unsteady flow. Nevertheless, this inventor maintains that this structure is a more rational starting base from which to make, or learn, those added allowances. Heretofore, research has not started with vane and side-wall structure representing in the first place, an inviscid steady-state source-vortex path in a vaneless diffuser. It is possible that those deleterious effects of viscosity and unsteady flow on performance may be found to be less than heretofore long established by experiment.